Electromagnetic conveyor system

ABSTRACT

A conveyor system for conveying electrically conductive articles such as aluminum cans. The conveyor system comprises a plurality of coils below the top surface of an electromagnetic conveyor at a junction between an infeed conveyor and a discharge conveyor. The coils propagate electromagnetic flux waves that induce currents in the electrically conductive articles that force the articles to follow a conveying path from the infeed to the discharge conveyor. Dead spots on the electromagnetic conveyor can be eliminated by adjusting the coil drive waveforms.

BACKGROUND

The invention relates generally to power-driven conveyors and more particularly to conveyors conveying electrically conductive articles, such as cans, electromagnetically.

Conveyors are used to transport articles through manufacturing processes. The transport of empty aluminum beverage cans can be difficult in transitions where the cans are transferred from one conveyor to another. The lightweight cans are prone to tipping at the transitions and to stranding on transfer dead plates. Manual intervention is required to deal with toppled and stranded cans. But manual intervention increases manufacturing costs and risks contamination of the cans. And if not dealt with, the stranding of cans can result in the costly mixing of can batches.

SUMMARY

One version of a conveyor system embodying features of the invention comprises a first conveyor conveying electrically conductive articles in a first direction to an exit end, a second conveyor conveying the electrically conductive articles from an entrance end in a second direction different from the first direction, and a diverter forming a junction between the exit end of the first conveyor and the entrance end of the second conveyor The diverter includes an entrance adjacent to the exit end of the first conveyor receiving the electrically conductive articles on a top surface from the exit end of the first conveyor and an exit adjacent to the entrance end of the second conveyor. Coils are arranged in a matrix of contiguous first and second zones below the top surface. The coils in each of the first zones produce an electromagnetic flux wave that forces the electrically conductive articles on the top surface above the zone to move in the first direction. The coils in each of the second zones produce an electromagnetic flux wave that forces the electrically conductive articles on the top surface above the zone to move in the second direction. At least some of the zones along the entrance are first zones and at least some of the zones along the exit are second zones. The electrically conductive articles are directed from the entrance to the exit by the coils in the first and second zones and onto the second conveyor.

Another version of a conveyor system embodying features of the invention comprises a first conveyor conveying electrically conductive articles in a first direction to an exit end and a second conveyor conveying the electrically conductive articles from an entrance end in a second direction. The angle θ between the first direction and the second direction is given by 0°<θ≤90°. A diverter forms a junction between the exit end of the first conveyor and the entrance end of the second conveyor. The diverter includes an entrance adjacent to the exit end of the first conveyor receiving the electrically conductive articles on a top surface from the exit end of the first conveyor and an exit adjacent to the entrance end of the second conveyor. Coils arranged in parallel below the top surface produce an electromagnetic flux wave that forces the electrically conductive articles on the top surface above the coils to move in a third direction. The angle a between the first direction and the third direction is given by 0°<α<θ. The electrically conductive articles are directed from the entrance to the exit by the coils and onto the second conveyor.

Yet another version of a conveyor system embodying features of the invention comprises a first conveyor conveying electrically conductive articles in a first direction to an exit end, a second conveyor conveying the electrically conductive articles from an entrance end in a second direction different from the first direction, and a diverter forming a junction between the exit end of the first conveyor and the entrance end of the second conveyor. The diverter includes an entrance adjacent to the exit end of the first conveyor receiving the electrically conductive articles on a top surface from the exit end of the first conveyor and an exit adjacent to the entrance end of the second conveyor. Coils are arranged in an arc below the top surface from the entrance to the exit. In a plan view perpendicular to the top surface, each of the coils has a narrow end at the inside of the arc and an opposite wider end at the outside of the arc. The electrically conductive articles are directed from the entrance to the exit by the coils and onto the second conveyor.

Another version of a conveyor system embodying features of the invention comprises an electromagnetic conveyor that includes an entrance over which electrically conductive articles are transferred onto a top surface and an exit over which electrically conductive articles are transferred off the top surface. Coils are arranged below the top surface in an array and produce electromagnetic flux waves causing forces that move the electrically conductive articles across the top surface from the entrance to the exit. A controller drives the coils with drive waveforms characterized by periodic pulses that periodically increase the forces acting on the electrically conductive articles in low-force regions on the top surface to enhance movement of the electrically conductive articles.

Still another version of a conveyor system embodying features of the invention comprises an electromagnetic conveyor that includes a top surface, an entrance over which electrically conductive articles are transferred onto the top surface, an exit over which electrically conductive articles are transferred off the top surface, and a plurality of coils arranged below the top surface in individual zones. The coils produce electromagnetic flux waves causing forces that move the electrically conductive articles through the zones across the top surface from the entrance to the exit. Controllers associated with the zones drive the coils with drive waveforms having different frequencies or phase angles in adjacent zones to enhance movement of the electrically conductive articles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a portion of a conveyor system embodying features of the invention for conveying electrically conductive articles, such as cans.

FIG. 2 is an isometric view of the conveyor system of FIG. 1 with the cans removed.

FIG. 3 is a top plan view of coil modules in a diverter as in the conveyor system of FIGS. 1 and 2.

FIGS. 4A and 4B include elevation and top plan views of adjacent coil modules in two different electromagnetic conveyors usable in a conveyor system as in FIG. 1.

FIG. 5 is a top plan view of an electromagnetic diverter with staggered coils in coil modules usable as an alternative diverter in the conveyor system of FIG. 1.

FIG. 6 is a top plan view of another version of a diverter having obliquely arranged coils alternatively usable in a conveyor system as in FIG. 1.

FIG. 7 is a top plan view of an alternative diverter with an arcuate arrangement of coils usable in a conveyor system as in FIG. 1.

FIG. 8 is a side elevation view of a coil as in FIG. 7 with a uniform core thickness and a varying winding thickness. FIGS. 8A and 8B are cross sections of the coil of FIG. 8 viewed along sight lines 8A and 8B.

FIG. 9 is a side elevation view of a coil as in FIG. 7 with a tapered core thickness.

FIG. 10 is a side elevation view of a coil as in FIG. 7 with a uniform core and winding thickness.

FIG. 11 includes top plan and side elevation views of a portion of an arcuate diverter as in FIG. 7, but with inner and outer coil sets.

FIG. 12 is a side elevation view of a coil winding usable in a conveyor system as in FIG. 1 with a winding crossover region along a short side.

FIG. 13 is a side elevation view of a coil winding usable in a conveyor system as in FIG. 1 with a winding crossover region along a long side.

FIG. 14 is a block diagram of a drive system for a conveyor system as in FIG. 1.

FIG. 15 shows one phase of a coil-drive waveform produced by the drive system of FIG. 14 using pulsed operation to eliminate dead spots.

FIG. 16 shows a portion of the waveform of FIG. 15 enlarged.

FIG. 17 shows corresponding phases of the coil-drive waveforms produced by the drive system of FIG. 14 for two adjacent coil zones to eliminate dead spots.

DETAILED DESCRIPTION

A conveyor system embodying features of the invention is shown in FIGS. 1 and 2. The conveyor system 20 has an infeed conveyor 22 and an outfeed, or discharge, conveyor 24—both shown as belt conveyors in this example. The infeed conveyor 22 conveys electrically conductive articles, such as aluminum cans 26, in a first conveying direction 28 to an electromagnetic conveyor 30. In this example the electromagnetic conveyor is configured as a diverting conveyor, or diverter, having an entrance 32 adjacent to an exit end 34 of the infeed conveyor. The discharge conveyor 24 receives the cans 26 at an entrance end 35 over an exit 33 of the diverter 30. In this example, the diverter 30 is rectangular—more precisely, square—with the entrance 32 and the exit 33 on adjacent sides. The discharge conveyor 24 conveys the cans 26 in a second conveying direction 29 different from the first conveying direction 28. The diverter 30 diverts the cans 26 on its top surface 36 from the first conveying direction 28 to the second conveying direction 29. In this example the diverter 30 serves as a 90° corner unit forming a junction between the exit end 34 of the infeed conveyor 22 and the entrance end 35 of the discharge conveyor 24. Although the infeed and outfeed conveyors 22, 24 are shown as belt conveyors in this example, they could be any kind of conveyor that is suitable for conveying the particular electrically conductive articles being handled. And the electromagnetic conveyor 30 can instead be configured as an in-line conveyor in which the cans are not turned, but pass straight through to a discharge conveyor in line with the infeed conveyor.

As FIG. 2 shows, the diverter 30 has a plurality of coils 38 arranged below the top surface 36 in a matrix of contiguous zones: first zones 40 and second zones 41. The coils 38 in the first zones 40 produce electromagnetic flux waves that force the cans in the first zones to move in the first conveying direction 28 as indicated by the arrows depicted in the zones. The coils 38 in the second zones 41 produce electromagnetic flux waves that force the cans in the second zones to move in the second conveying direction 29. The electromagnetic flux waves produced by the coils 38 in both zones 40, 41 propagate in the corresponding first or second conveying direction 28, 29 and induce currents in the electrically conductive cans 26. The induced currents produce induced secondary fields that interact with the primary fields of the flux waves to create the force acting on the cans to move them in the corresponding direction. Thus, the coils 38 in each zone serve as the stator of a linear induction motor (LIM) in which each of the electrically conductive cans 26 is analogous to a LIM rotor.

Although the first and second zones 40, 41 in the diverter 30 can be of different lengths as in FIG. 2, each zone can be constructed of one or more identical coil modules 42, 42′, as shown in FIG. 3. Coils in each coil module 42, 42′ are housed in an enclosure or are embedded in a potted structure. The upper surfaces of the enclosures or structures can form the top surface 36 of the diverter 30 if they fit close together with narrow seams between adjacent coil modules 42, 42′ to avoid tipping the cans 26. The top surface 36 of the diverter 30 can alternatively be formed by a sheet or other structure providing a flat conveying surface covering the coil modules 42, 42′. First coil modules 42 form the first zones 40, and second coil modules 42′ form the second zones 41.

In this example the matrix of contiguous first and second zones 40, 41 is a square matrix of the identical coil modules 42, 42′ arranged in four rows R1-R4 and four columns C1-C4. The rows R1-R4 are aligned in the second conveying direction 29 and perpendicular to the first conveying direction 28, and the columns C1-C4 are aligned in the first conveying direction and perpendicular to the second conveying direction. Furthermore, in this example, there are eleven second coil modules 42′ forcing cans in the second direction 29 toward the exit 33 of the diverter 30 and five coil modules 42 forcing cans in the first direction 28 away from the entrance 32. The coil module 42′ in the row R1 closest to the entrance 32 and the column C4 closest to the exit 33 is in a second zone 41. And all the coil modules 42′ in the column C4 closest to the exit 33 are in second zones 41. Three of the four coil modules in the row R1 closest to the entrance 32 of the diverter 30 are in first zones 40.

In this particular arrangement of coil modules 42, 42′ and zones 40, 41, the number of coil modules in contiguous first zones 40 decreases monotonically row by row away from the entrance 32. (The row R1 closest to the entrance 32 has three coil modules 42 in first zones 40; the next row R2 has two; and the third and fourth rows R3, R4 have none.) Cans fed onto the left side of the diverter 30 at the entrance 32 are pushed in the first zones 40 in the leftmost columns C1, C2 toward the second zones 41 in the far rows R3, R4. Cans immediately to the right of those are pushed in the first zone 40 on the entrance row R1 and the third column C3 to the second zone 41 in the second row R2. Cans fed onto the diverter 30 along its right side 45 and received in the second zone 41 are pushed immediately toward the exit 33. In this way cans closer to the right side 45 of the diverter 30 make a sharper turn to the right than those cans closer to the left side to help maintain the width of the mass of cans.

Of course, other arrangements of the zones and coil modules are possible. For example, the coil module in the first row R1 and the fourth column C4 could be in a first zone to help induce cans onto the diverter 30 before their direction is changed. As another example, the matrix of zones could be arranged as a non-square rectangular array of coil modules. Or each zone could be made of a single coil module whose length defines the length of the zone. And the number of zones and coil modules could be greater or less than shown in FIGS. 1-3. An in-line electromagnetic conveyor is constructed with all the coil modules in a single zone or in multiple zones all directing cans in the same direction from the entrance to an opposite exit without a change in direction.

FIGS. 4A and 4B show two different side-by-side coil arrangements as part of a diverter or as all or part of an in-line conveyor. FIG. 4A shows two side-by-side coil modules 42A, 42B in adjacent zones Z1, Z2. Each coil 46 is wound around a core 48: for example, a laminated iron core such as a silicon-iron (SiFe) core. In this example each coil module 42A, 42B has six coils 46. Opposite ends of the cores 48 have a stepped structure of alternating protrusions 50 and recesses 52 that mate with the protrusions and recesses of the core of an adjacent coil module to form a longer zone. The coils 46 on each core 48 are spaced apart across gaps 54. The ends of the coils 46 of side-by-side coil modules 42A, 42B are offset along the coils' magnetic axes 55 to fit in the gaps 54. The resulting overlap of the coil ends helps eliminate dead spots in low-force regions in the diverter. FIG. 4B shows two side-by-side coil modules 42A′, 42B′ in adjacent zones Z1, Z2. The coils 46 in each zone Z1, Z2 are wound around a single core and are closely spaced so that little of the core is uncovered by the windings. The coils 46 in the adjacent zones Z1, Z2 are individually side by side with no axial offset and do not overlap the ends of the coils in the abutting laterally adjacent zone.

FIG. 5 shows an alternative diverter 60 arrangement of staggered first and second zones 56, 57. Cans in the first zones 56 are moved in the first conveying direction 28 by the coils 46, and cans in the second zone 57 are moved in the second conveying direction 29. An oblique line of demarcation 62 separates the first zones 56 from the second zones 57. Each module 58 is parallelogram-shaped. The coils 46 in each module 58 are offset lengthwise from each other to form the stagger along lines parallel to the demarcation line 62 and oblique to the first and second conveying directions 28, 29. The staggered zones 56, 57 reduce low-flux areas in the diverter 60 compared to the rectangular zones in the diverter 30 of FIGS. 1-4.

Another version of an electromagnetic diverter for electrically conductive articles is shown in FIG. 6. In this version all the coils 64 in the diverter 66 are arranged geometrically with their magnetic axes 65 parallel and oblique to the first and second conveying directions 28, 29. The flux wave produced by the oblique coils 64 travels in a third direction 68 oblique to the first and second directions 28, 29. The angle θ between the first and second directions 28, 29 is given by 0°<θ≤90°. In this example, θ=90°. The angle α between the first and third directions 28, 68 is given by 0°<α<θ. Cans fed onto the diverter 66 are immediately pushed diagonally toward the discharge conveyor 24 in the third direction 68.

Yet another version of an electromagnetic diverter is shown in FIG. 7. The diverter 70 defines a curved track. In this example the curved track is an arc subtending a 90° angle. Each of the coils 72 has a narrow end 74 at an inside of the arc and a wider end 75 at the outside of the arc. The coils 72 are driven by a three-phase coil drive according to the A-B-C phasing arrangement φ1. One alternative is driving the coils with an apparent six-phase coil drive sequence φ2, which can be achieved with a three-phase coil driver by alternating the winding polarities as indicated by the φ2 phase sequence.

FIGS. 8-10B show cross sections of alternative coils usable in the curved-track diverter 70 of FIG. 7. The coil 84 in FIG. 8 has a laminated core 86 of uniform thickness, i.e., constant height, along its length. As shown in the cross sections of the coil 84 in FIGS. 8A and 8B, the inside end 74 is laterally narrower than the wider outside end 75 and the narrow inside end 74 is taller than the wider outside end 75. The coil windings at the narrow inside end require more layers than at the wider outside end to keep a constant number of turns of a uniformly thick wire.

In FIG. 9 the stack of iron-core laminations 76 is tapered in thickness (height). The thickness T increases from the inside end 74 of the coil 78 to the outside end 75. Because the coil 78 is generally trapezoidal in a plan view—wider at the outside end 75 than at the inside end 74—the windings at the outside are distributed over a greater distance laterally, and so the depth of the winding layers is less to form the coil with a constant outer thickness (height) along its length.

Another alternative coil 80 is shown in FIG. 10. Like the coil 78 of FIG. 9, the coil 80 has a constant thickness (height) along its length. And the thickness T of the coil's laminated core 82 is also uniform along its length so that the ratio of the thickness of the coil to the thickness of the iron core is constant along the length of the coil 80. Because the outside end 75 of the coil 80 is wider, the coil windings are distributed laterally over a greater width and are not as deep as the winding layers at the narrower inside end 74.

FIG. 11 shows a portion of a curved diverter as an alternative to that of FIG. 7. The diverter 90 is constructed of two concentric arcs 92, 92 of coils 94, 95. (Only three coils are shown in each arc to simplify the drawing.) The inner arc 92 lies inside the outer arc 93.

As shown in FIGS. 12 and 13, the coils 96, 96′ for all the examples can be orthocyclically wound to minimize the volume occupied by the windings. In the rectangular coil configuration shown, the orthocyclic crossover region of the coils is confined to one side of the coil. In FIG. 12 the crossover region 98—i.e., the region where the windings cross over each other to achieve the tight packing of orthocyclic windings—is formed on one of the short sides. In FIG. 13 the crossover region 99 is formed on one of the long sides, such as the bottom side away from the top surface of the diverter to minimize the gap between the iron core and the conveyed articles and to minimize dead spots in the low-force boundary regions along the short sides of laterally adjacent coils where the net field strength required to move cans is low. The coils 96, 96′ in FIGS. 12 and 13 have magnetic axes 97 directed along the length of the coils' cores and parallel to the top surface of the diverter.

A controller for driving the coils in all the examples is shown in FIG. 14. The controller 100 is a multiphase controller shown in this example as a three-phase controller operating as three current sources driving the coils 102A-C in each phase A, B, C through coil drivers 104A-C and series capacitors 105A-C. Each zone in the diverters of FIGS. 1-6 or in an in-line electromagnetic conveyor could have a dedicated controller. All the first zones of diverters could be driven electrically in parallel by a first single controller, and all the second zones could be driven by a second single controller. In-line conveyors and the diverters in FIGS. 6 and 7 could be driven by a single dedicated multiphase controller. And each arc in the diverter in FIG. 11 could be driven by its own multiphase controller.

A programmable processor 106 connected to the controller 100, can be connected to other such controllers to coordinate control of all the coil zones. Or the processor 106 could be integrated into each controller 100 instead. A vision system 108 including one or more cameras capturing digital images of the cans 26 in the zones on the conveyor 20 sends the captured images to the processor 106. From the images the processor 106 can detect stranded cans and flow problems and alter the normal coil drive sequence to remedy any problems. For example, one way that dead spots on a diverter or an in-line conveyor can be eliminated is by driving the coils with a waveform as shown in FIGS. 15 and 16. The standard ac drive waveform 110 for each phase is amplitude-modulated by a pulse train to produce periodic higher-power drive pulses 112. The periodic pulses can occur at fixed or varying rates. For example, FIGS. 15 and 16 show a 1 kHz drive waveform modulated by a fixed 8.3 Hz pulse train with a 17% duty cycle and a pulse-amplification factor of about 1.2. The capacitance C of the series capacitors 105A-C is selected to form a high-Q resonant circuit with the large inductance L of the coils 102A-C in each phase. The frequency f of the ac drive waveform 110 for each phase is set close to the circuit's nominal resonant frequency f_(r)=1/[2π(LC)^(1/2)]. Because of tolerances in the actual values of L and C and the fact that the coil drivers operate better driving inductive loads, the frequency f of the ac drive waveform is set close to, but slightly above, the nominal, or theoretical, resonant frequency f_(r). The frequency f of the ac drive waveform is set high enough above the nominal resonant frequency f_(r) to ensure that the reactive impedances X of all the coil circuits are positive, i.e., inductive, and that the drive frequency f is close to the circuit's actual resonance frequency—at least as close as the resonant circuit's upper half-power (3 dB) frequency—for any combination of coils and capacitors. In that way deviations and variations in the inductances and capacitances from their nominal values are accounted for, and the reactive impedances X do not dominate the resistive impedances R, i.e., |X|/R<1.73, or, in other words, the power factor is greater than 0.5. Coil drivers designed to drive capacitive loads with a drive waveform whose frequency f is slightly below the resonant frequency f_(r) could alternatively be used in an analogous way to ensure that the reactive impedances X of all the coil circuits are negative, i.e., capacitive, and not dominant, and that the drive frequency f is close to the circuit's actual resonant frequency. As another alternative, one of ordinary skill in the art would be able to design a conventional closed-loop system to drive the coils at exactly the resonant frequency f_(r), for which the reactive impedance X would be zero. Any of these resonant coil-driving schemes results in a non-dominant, zero or low reactive impedance and an efficient transfer of power to the coils. Exemplary pulse-repetition rates range from about 5 Hz to 20 Hz with a duty-cycle range of about 5% to 20%. Exemplary pulse-amplification factors range from about 1.2 to 1.5 or greater. The higher-amplitude coil-drive pulses 112 produce periodic increases in the magnetic field and the forces acting on cans slowed or stopped in otherwise low field-strength and force (dead spot) regions to move the cans. The pulsed operation can be run at a fixed pulse frequency and duty cycle, or the processor 106 can direct the controller 100 to produce drive pulses that clear the dead spot and otherwise enhance can movement when a stranded or slow-moving can is detected by the vision system 108. The advantage of applying short pulses to the ac drive waveform rather than operating permanently at a fixed, greater amplitude is that the short pulses free the stranded cans without significantly increasing the speed of the unstranded, moving cans, which can result in tipping.

Another way of eliminating dead spots is by driving the coils in adjacent zones with phase-shifted waveforms as shown in FIG. 17. The upper waveform 114 represents the coil drive for one phase in a first zone; the lower waveform 116 represents the coil drive for the corresponding phase in an adjacent zone. The phases of the two waveforms differ by a phase angle θ, about 90° in this example. And the same phase shift would exist between the other phases in a multiphase system. The phase shift between the drive waveforms of adjacent zones clears cans from dead spots by creating a component of force that is perpendicular to the main conveying direction as a result of the interaction of the out-of-phase electromagnetic flux waves. The perpendicular component of force clears the dead spots between the adjacent zones. As in the other dead-spot-clearing techniques, the phase difference can be fixed or adjusted by the processor 106 when stopped or slow-moving cans are detected by the vision system 108.

Yet another way that dead spots can be eliminated is by operating coils in adjacent zones at different frequencies. For example, the coils in one zone could be driven by an 1100 Hz waveform and those in an adjacent zone by an 1102 Hz waveform. Like driving the coils in adjacent zones with a phase shift, driving the coils at different frequencies produces a force acting on the cans in a direction perpendicular to the conveying direction. The frequency difference can be fixed or can be imposed by the processor 106 when stranded cans are detected by the vision system 108.

All the dead-spot-clearing techniques are usable with electromagnetic diverters or with in-line or diverting electromagnetic conveyors to ensure the efficient conveyance of cans from the infeed conveyor to the discharge conveyor.

Aluminum cans were used throughout the description as exemplary electrically conductive conveyed articles. But other electrically conductive articles containing electrically conductive material, such as aluminum or copper, could be conveyed by the coils described. 

1. A conveyor system comprising: a first conveyor conveying electrically conductive articles in a first direction to an exit end; a second conveyor conveying the electrically conductive articles from an entrance end in a second direction different from the first direction; a diverter forming a junction between the exit end of the first conveyor and the entrance end of the second conveyor; wherein the diverter includes: a top surface; an entrance adjacent to the exit end of the first conveyor receiving the electrically conductive articles on the top surface from the exit end of the first conveyor; an exit adjacent to the entrance end of the second conveyor; a plurality of coils arranged in a matrix of contiguous first and second zones below the top surface, wherein the coils in each of the first zones produce an electromagnetic flux wave that travels in the first direction and forces the electrically conductive articles on the top surface above the zone to move in the first direction and the coils in each of the second zones produce an electromagnetic flux wave that travels in the second direction and forces the electrically conductive articles on the top surface above the zone to move in the second direction, wherein at least some of the zones along the entrance are first zones and at least some of the zones along the exit are second zones; wherein some of the coils in the diverter are in the first zones and the rest of the coils are in the second zones; wherein the electrically conductive articles are directed from the entrance to the exit by the coils in the first and second zones and onto the second conveyor.
 2. (canceled)
 3. A conveyor system as in claim 1 wherein the second direction is perpendicular to the first direction.
 4. A conveyor system as in claim 1 wherein the coils in each of the zones are staggered along parallel lines oblique to the first and second directions.
 5. A conveyor system as in claim 1 wherein each of the first and second zones includes a single coil module having a single iron core along which all the coils in the zone are wound.
 6. A conveyor system as in claim 1 wherein each of the first and second zones includes one or more coil modules, each having the same number of coils.
 7. A conveyor system as in claim 6 wherein each of the coil modules includes an iron core around which the coils are formed and wherein the iron core in at least some of the coil modules has a stepped structure along at least one end that mates with the stepped structure on the iron core of an adjacent coil module in the same zone.
 8. A conveyor system as in claim 6 wherein the coils in the adjacent coil modules of different first zones or different second zones overlap each other.
 9. A conveyor system as in claim 6 wherein the matrix of contiguous first and second zones is a rectangular matrix of the coil modules.
 10. A conveyor system as in claim 6 wherein the matrix of contiguous first and second zones defines rows of coil modules aligned in the second direction and columns of coil modules aligned in the first direction.
 11. A conveyor system as in claim 10 wherein the number of coil modules in contiguous first zones decreases monotonically row by row away from the entrance.
 12. A conveyor system as in claim 1 wherein the coils are rectangular with two short sides and two long sides and have a magnetic axis parallel to the top surface and are orthocyclically wound with a crossover region along one of the sides.
 13. A conveyor system as in claim 12 wherein the crossover region is along the long side farther from the top surface of the diverter.
 14. A conveyor system as in claim 1 comprising a multiphase controller driving the coils in each of the first and second zones.
 15. A conveyor system comprising: a first conveyor conveying electrically conductive articles in a first direction to an exit end; a second conveyor conveying the electrically conductive articles from an entrance end in a second direction, wherein the angle θ between the first direction and the second direction is given by 0°<θ≤90°; a diverter forming a junction between the exit end of the first conveyor and the entrance end of the second conveyor; wherein the diverter includes: a top surface; an entrance adjacent to the exit end of the first conveyor receiving the electrically conductive articles on the top surface from the exit end of the first conveyor; an exit adjacent to the entrance end of the second conveyor; a plurality of coils arranged in parallel below the top surface and having magnetic axes in a third direction oblique to the first direction and producing an electromagnetic flux wave that forces the electrically conductive articles on the top surface above the coils to move in the third direction, wherein the angle a between the first direction and the third direction is given by 0°<α<θ; wherein the electrically conductive articles are directed from the entrance to the exit by the coils and onto the second conveyor.
 16. A conveyor system as in claim 15 wherein θ=90°.
 17. A conveyor system as in claim 15 comprising a multiphase controller driving the coils.
 18. A conveyor system comprising: a first conveyor conveying electrically conductive articles in a first direction to an exit end; a second conveyor conveying the electrically conductive articles from an entrance end in a second direction different from the first direction; a diverter forming a junction between the exit end of the first conveyor and the entrance end of the second conveyor; wherein the diverter includes: a top surface; an entrance adjacent to the exit end of the first conveyor receiving the electrically conductive articles on the top surface from the exit end of the first conveyor; an exit adjacent to the entrance end of the second conveyor; a plurality of coils arranged in an arc below the top surface from the entrance to the exit wherein, in a plan view perpendicular to the top surface, each of the coils has a narrow end at the inside of the arc and an opposite wider end at the outside of the arc; wherein the electrically conductive articles are directed from the entrance to the exit by the coils and onto the second conveyor.
 19. A conveyor system as in claim 18 wherein the arc subtends an angle of 90°.
 20. A conveyor system as in claim 18 wherein the narrow end of the coil is taller than the wider end in a direction perpendicular to the top surface.
 21. A conveyor system as in claim 18 comprising an iron core around which the coil is formed and wherein the thickness of the iron core is constant along the length of the coil.
 22. A conveyor system as in claim 18 comprising iron cores around which the coils are formed, wherein the thickness of the iron cores increases from the end of the coils at the inside of the arc to the end of the coils at the outside of the arc.
 23. A conveyor system as in claim 18 comprising iron cores around which the coils are formed, wherein the ratio of the thickness of the coils to the thickness of the iron cores is a constant along the lengths of the iron cores.
 24. A conveyor system as in claim 18 comprising an iron core around which the coil is formed, wherein the thickness of the iron core is constant along its length.
 25. A conveyor system as in claim 18 wherein the coils are orthocyclically wound with the crossover region at the end of the coil closer to the inside of the arc.
 26. A conveyor system as in claim 18 wherein the arc of coils forms an outer arc and the conveyor system comprises a second plurality of coils arranged in an inner arc inside the outer arc.
 27. A conveyor system as in claim 18 comprising a multiphase controller driving the coils.
 28. A conveyor system comprising: an electromagnetic conveyor including: a top surface; an entrance over which electrically conductive articles are transferred onto the top surface; an exit over which electrically conductive articles are transferred off the top surface; a plurality of coils arranged below the top surface in an array and producing electromagnetic flux waves causing forces that move the electrically conductive articles across the top surface from the entrance to the exit; a controller driving the coils with drive waveforms characterized by a first amplitude and periodic pulses of a greater second amplitude that periodically increase the forces acting on the electrically conductive articles in low-force regions on the top surface to enhance movement of the electrically conductive articles from low-force regions on the top surface.
 29. A conveyor system as in claim 28 wherein the controller drives the coils with the periodic pulses at a fixed rate.
 30. A conveyor system as in claim 28 wherein the periodic pulses are formed by modulating the amplitude of the drive waveforms.
 31. A conveyor system as in claim 28 further comprising a capacitor in series with the controller and the coils to form a resonant circuit with the coils with a resonant frequency and wherein the frequency of the drive waveform is close enough to the resonant frequency to ensure that the reactive impedance of the resonant circuit is not dominant.
 32. A conveyor system as in claim 28 further comprising: a processor; and a vision system capturing digital images of the electrically conductive articles being conveyed on the top surface of the electromagnetic conveyor and sending the digital images to the processor; wherein the processor directs the controller to drive the coils with the drive waveforms characterized by periodic pulses whenever stopped or slowed articles are detected in the digital images.
 33. A conveyor system comprising: an electromagnetic conveyor including: a top surface; an entrance over which electrically conductive articles are transferred onto the top surface; an exit over which electrically conductive articles are transferred off the top surface; a plurality of coils arranged below the top surface in individual zones and producing electromagnetic flux waves causing forces that move the electrically conductive articles through the zones across the top surface from the entrance to the exit; controllers associated with the zones and driving the coils with drive waveforms having different frequencies or phase angles in adjacent zones to enhance movement of the electrically conductive articles from zone to zone.
 34. A conveyor system as in claim 33 wherein the controllers drive the coils with the drive waveforms having fixed different frequencies or fixed phase angles.
 35. A conveyor system as in claim 33 further comprising capacitors in series with the controllers and the coils to form resonant circuits with the coils with resonant frequencies and wherein the frequencies of the drive waveforms are close enough to the resonant frequencies to ensure that the reactive impedances of the resonant circuits are not dominant.
 36. A conveyor system as in claim 33 further comprising: a processor; and a vision system capturing digital images of the electrically conductive articles being conveyed on the top surface of the electromagnetic conveyor and sending the digital images to the processor; wherein the processor directs the controller to drive the coils with the drive waveforms having different frequencies or phase angles in adjacent zones whenever stopped or slowed articles are detected in the digital images. 